الفهرس 
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Abstract
The increasing of global demand and decreasing availability of fish had led to sharp increase in the price of fish meal (FM) and the cost of aquaculture production. As a result, developing practical diets using cheap sustainable alternative non-FM protein sources are needed. Consequently, the present study was planned to evaluate the partial (25, 50 and 75%) or total (100%) substitution of dietary FM with Procambarus clarkii by-product meal (PBM) for Nile tilapia, Oreochromis niloticus fingerlings as a cheap sustainable alternative non-FM protein source.
In the present experimental trial, five isonitrogenous (30% protein) experimental diets were formulated; diet 1 contained FM which was considered as the control diet, diets 2, 3, 4 and 5 were 25, 50, 75 and 100% substitution of FM with the PBM, respectively. Each diet was given to O. niloticus in duplicate groups for four months.
The present study revealed that the protein content of PBM was 33.13% and its amino acids profile fulfilled the requirements of O. niloticus. All analysed heavy metals of PBM, except arsenic and iron, were in the permissible limits for O. niloticus.
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With respect to the chemical composition of O. niloticus
carcass, the present study revealed that there was significantly increased in body moisture and ash of fish of all treated groups in comparable with the control group. The final protein and lipid contents of the control diet, D2 and D3 showed the highest contents, while D4 and D5 showed the lowest contents. Moreover, there was a significant decrease in lipid content of fish that fed D2, D3, D4, and D5 in comparable to fish that fed the control diet.
Regarding to the growth performance of O. niloticus, the present investigation demonstrated that the weight gain and specific growth rate of fish of all treated groups were significantly lower than those of the control one. The highest weight gain and specific growth rate were recorded in the control diet, D2 and D3, while the lowest values were recorded for fish that fed D4 and D5.
The results of the present work revealed that the feed utilization of the O. niloticus decreased as the level of the substitution of FM by PBM increased. The feed conversion ratio, feed efficiency ratio and protein efficiency ratio of fish that fed D2 and D3 were insignificantly different in comparable with the control group, while, there were
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significant differences of fish that fed D4 and D5 in comparable with the control group.
In the present work, the histological examination showed that the liver of O. niloticus was the lowest affected organ; fish that fed the control diet and D2 did not show any histological changes, while the liver tissue of fish that fed D3 and D4 show slight histopathological signs. However, O. niloticus that fed D5 revealed severe lipid depletion, sinusoidal blood congestions and necrotic hepatocytes. The kidney was moderately affected organ; fish that fed the control diet, D2 and D3 did not show any remarkable histological alterations, while D4 and D5 showed severe blood congestion, tubular degeneration and glomerular atrophy. The gills were the most affected organ in all treated groups; they showed hyperplasia of gill filament epithelium, epithelial lifting, fusion of gill lamellae, degeneration of pavement cells and lamellar aneurysm.